Weather and hydrographic conditions associated with coral bleaching: Lee Stocking Island, Bahamas

Thermograph, current-meter, and coastal-weather data from Lee Stocking Island, Exuma Cays, Bahamas, are used to investigate hydrographic and meteorological conditions preceding and during a bleaching event in August 1990. Shelf water temperatures recorded at three locations rise to just over 30degreesC. Weather data provide estimates of local heating and cooling by insolation, net outgoing long-wave radiation, and sensible and latent heat fluxes. Weather data do not indicate a period of unusually clear skies during the days and weeks preceding the bleaching event. Rather, calculations suggest that low wind speeds during late July and early August reduced evaporative cooling. A tidal channel near the bleaching site provided a source of hyperpycnal 31degreesC water that had been heated in the shallow waters of Great Bahama Bank. Current-meter data suggest an along-shelf transport of water from the mouth of the tidal channel to the bleaching site. A comparison of wind-stress and water-temperature data suggests that a downwelling pattern contributed to heating at the reef by flooding the shelf with warm surface water. Results suggest that heating at the reef was a combination of local warming, enhanced by reduced evaporation, and advective warming resulting from both an along-shelf transport of bank water and a landward across-shelf transport of warm surface water.